One type of circuitry device is a field effect transistor. Typically, such includes opposing semiconductive material source/drain regions of one conductivity type having a semiconductive channel region of opposite conductivity type therebetween. A gate construction is received proximate the channel region between the source/drain regions. The gate construction typically includes a conductive region and a thin dielectric layer positioned between the conductive region and the channel region. Current can be caused to flow between the source/drain regions through the channel region by applying a suitable voltage to the conductive portion of the gate.
In certain fabrication methods, different sets of field effect transistors are fabricated at different times. For example in CMOS circuitry, different conductivity-type transistors are fabricated. It is common for the different types of transistors to be fabricated separately, or at least partially at different times, to provide the desired conductivity-type and dopant concentrations for the respective transistors. For example in some such instances, a common conductive gate layer is separately masked and exposed on different areas of the wafer for fabricating the desired gates at different times and locations on the wafer for the different conductivity-type transistors.
The most common technique still utilized today for transistor gate fabrication is photolithography and etch. The ever-reducing size of the device components is resulting in an increase in the vertical heights of the etched devices as compared to their widths, something referred to as “aspect ratio”. It is highly desirable that the width/critical dimension of the smallest features be controlled in the given photomasking and etching steps such that it is constant over the substrate. Yet, differing topography across the wafer when fabricating the gate stacks for transistors can result in less than desired control and consistency in device critical dimension which are fabricated over the wafer in the same masking step.
The invention was principally motivated in addressing the above-described issues and problems, although it is in no way so limited. The artisan will appreciate the applicability of the invention outside of the environment in which the invention was motivated. The invention is only limited by the accompanying claims as literally worded, without interpretative or other limiting reference to the specification, and in accordance with the doctrine of equivalents.